Catalysts, reactors and methods of producing hydrogen via the water-gas shift reaction

ABSTRACT

The reaction of carbon monoxide with steam over an alkali-modified ruthenium-on-zirconia catalyst has been found to yield surprisingly high yields of hydrogen gas at relatively low temperatures. Catalyst structures, reactors, hydrogen production systems, and methods for producing hydrogen utilizing the alkali-modified ruthenium-on-zirconia catalyst are described. Methods of making catalysts are also described.

FIELD OF THE INVENTION

The invention relates to catalysts, reactors and methods of producinghydrogen from the water gas shift reaction.

INTRODUCTION

Hydrogen gas (H₂) can be readily produced from synthesis gas (syngas) bysteam reforming, or partial oxidation, or autothermal reforming ofhydrocarbons. Additional H₂ is then produced by allowing syngas to reactwith steam according to the following exothermic water gas shiftreaction (WGSR):CO+H₂O=H₂+CO₂The thermodynamics of WGSR are well known. The equilibrium constant ofthis reaction increases as temperature deceases. Hence, to increase theproduction of H₂, it is desirable to conduct the reaction at lowertemperatures, which are also preferred from the standpoint of steameconomy.

Two types of commercially available WGSR catalysts are: iron-based hightemperature (HT) shift and copper-based low temperature (LT) shiftcatalysts with Cu based catalysts being relatively more active. However,both catalysts are not very active under their applicable conditions asindicated by their operational contact times (contact time is defined ascatalyst bed volume divided by volumetric gas feed flowrate at standardtemperature and pressure) of several seconds. Longer contact times implythe requirement of large catalyst bed volume. Operating at shortercontact times with these commercial catalysts requires higher reactiontemperatures, which not only accelerates catalyst deactivation due tometal sintering but also disfavors the thermodynamics of the WGSR, asmentioned above.

SUMMARY OF THE INVENTION

It has been discovered that the use of a zirconia-supported,alkali-metal-modified, ruthenium catalyst in the water gas shiftreaction produces unexpectedly superior results.

In one aspect, the invention provides a catalyst comprising: a poroussubstrate having an average pore size of from 1 μm to 1000 μm, and,disposed over the porous substrate, a zirconia-supported,alkali-metal-modified, ruthenium catalyst.

The catalyst can be made by wash-coating zirconia-supportedalkali-metal-modified ruthenium catalyst on a porous substrate. Zirconiasupported alkali-metal modified ruthenium catalyst can be prepared, forexample, using the incipient wetness method.

In a related aspect, the invention provides a new method of producinghydrogen gas. In this method, a reactant gas mixture comprising carbonmonoxide and water vapor is contacted with the zirconia-supported,alkali-metal-modified, ruthenium catalyst.

The invention also provides a reactor containing the inventive catalyst.Typically, the reactor contains a reactor inlet, a reaction chamber, anda reactor outlet. It is particularly advantageous for the reactor toalso contain a microchannel heat exchanger in thermal contact with thereaction chamber. The microchannel heat exchanger enables rapid heattransfer from the reaction chamber thus allowing the inventive catalystto operate at near isothermal and low temperature conditions to maximizeCO2 selectivity while maintaining high conversions of carbon monoxide.

Another related aspect of the present invention is the use of thecatalyst in a hydrogen production system. For example, the inventionincludes a fuel system containing the above-described reactor. Inanother aspect, the invention provides a hydrogen production systemhaving a fuel source (preferably a liquid fuel tank); a primaryconversion reactor (where a process such as steam reforming, partialoxidation, or autothermal reforming is conducted) to produce a gasmixture containing hydrogen, carbon dioxide, and carbon monoxide; and awater gas shift reactor. The water gas shift reactor includes a shiftreactor inlet, a reaction chamber, and a shift reactor outlet. The shiftreactor inlet is connected to the primary conversion reactor exhaustoutlet such that carbon-monoxide-containing exhaust from the primaryconversion reactor is fed into the shift reactor. The reaction chambercontains a zirconia-supported, alkali-metal-modified, rutheniumcatalyst.

Various embodiments of the invention can provide numerous advantagesincluding one or more of the following: high carbon monoxideconversions, high carbon dioxide selectivity, low methane selectivity,operation at short contact times, and low temperature operation.

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of this specification.However, both the organization and method of operation, together withfurther advantages and objects thereof, may best be understood byreference to the following description taken in connection withaccompanying drawings wherein like reference characters refer to likeelements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of CO conversion (♦) and CO₂ selectivity (▪) vs.temperature for the reaction of a gas mixture consisting of 8% CO, 7%CO₂, 38% H₂, and 47% H₂O, over a powder Ru/ZrO₂ catalyst, at a 25millisecond (ms) contact time.

FIG. 2 is a plot of CO conversion (♦), CH₄ selectvity (▴), and C0 ₂selectivity (▪) vs. temperature for the reaction of a gas mixtureconsisting of 8% CO, 7% CO₂, 38% H₂, and 47% H₂O, over a powder 0.5 wt%Ru-1.5 wt %K/ZrO₂ catalyst, at a 25 ms contact time.

FIG. 3 is a plot of CO conversion (♦, ▴) and CO₂ selectivity (⋄, Δ) vs.temperature for the reaction of a gas mixture consisting of 8% CO, 7%CO₂, 38% H₂, and 47% H₂O, over a 0.5 wt %Ru-1.5 wt %K/ZrO₂/(felt (♦, ⋄)or foam (▴, Δ)) catalyst, at a 50 ms contact time.

FIG. 4 is a schematic of a simplified fuel cell system that includes across-sectional view of a water gas shift reactor that includes amicrochannel heat exchanger.

FIG. 5 is a schematic view of an interleaved microchannel reactororiented in a co-current flow configuration.

DETAILED DESCRIPTION OF THE INVENTION

The reaction of carbon monoxide (CO) and water vapor (H₂O) overruthenium on zirconia (Ru/ZrO₂) at short contact times (<1 s) was foundto produce hydrogen (H₂) in good yields when hydrogen is not present inthe reactant mixture. However, attempts to produce hydrogen from carbonmonoxide and water at low contact times over a ruthenium on zirconia(Ru/ZrO₂) catalyst in the presence of hydrogen gas were foundunsatisfactory because at high CO conversions, very little carbondioxide was produced. Instead, methane formed in the undesiredmethanation side reaction:CO+6H₂=CH₄+H₂OAn example of results from reaction of a gas mixture consisting of 8%CO, 7% CO₂, 38% H₂, and 47% H₂O, (unless specified otherwise, gasmixtures are reported in volumetric percents) over a powder 5 wt%Ru/ZrO₂ catalyst, at a 25 millisecond (ms) contact time, is illustratedin FIG. 1. As can be seen in the figure, at 350° C., the conversion ofCO is about 90% but the selectivity to carbon dioxide is less than 30%.Thus, there was a formidable challenge to develop a highly selective,yet active catalyst for the water gas shift reaction.

It was surprisingly discovered that greatly improved results could beobtained by use of a zirconia-supported, potassium-modified, rutheniumcatalyst. An example of results from reaction of a gas mixtureconsisting of 8% CO, 7% CO₂, 38% H₂, and 47% H₂O, over a powder 0.5 wt%Ru-1.5 wt %K/ZrO₂ catalyst, at a 25 ms contact time, is illustrated inFIG. 2. As can be seen in the figure, at a catalyst bed temperature ofabout 420° C., the conversion of CO reaches about 85% while theselectivity to carbon dioxide is greater than 90%.

It was subsequently discovered that distributing the zirconia-supported,potassium-modified, ruthenium over a large pore substrate can yield evenbetter results. For example, FIG. 3 shows CO conversion and selectivityto CO₂ on a 0.5 wt % u-1.5 wt %K/ZrO₂/felt catalyst in which the 0.5 wt%Ru-1.5 wt %K/ZrO₂ powder has been deposited on a FeCrAlY felt having athickness of 0.01 inch (0.25 mm) inserted into a single channel having awidth of 0.03 inch (0.76 mm). At a contact time of 50 ms and atemperature of about 300° C. the felt catalyst gives higher than 85% COconversion with near 100% CO₂ selectivity. The felt form (having asubstrate made of randomly interwoven FeCrAlY strands) was found toperform better than the foam form (having a substrate made of astainless steel foam).

Catalysts of the present invention include ruthenium metal, an alkalimodifier and a zirconium oxide (zirconia), preferably ZrO₂ althoughvariation from this stiochiometry is acceptable, especially in light ofthe alkali modifier. Thus far, only potassium (K) has been tested as thealkali modifier; however, it is believed that the primary effect of thealkali modifier is to reduce the hydrogen chemisorption, and thereforeit is believed that other alkali metals, would also be effectivemodifiers.

The catalyst preferably contains 0.1 wt % to 10 wt %, more preferably0.2% to 3% weight percent Ru. The Ru should be dispersed over the ZrO₂surface. Too little Ru can result in too few catalytic sites, while toomuch Ru is costly due to lower Ru dispersion. The alkali metal,preferably K, is preferably present in a range of 0.1 to 10, morepreferably 0.5 to 3 weight percent. Too little alkali metal can resultin undesirably low CO₂ selectivity while too much alkali metal couldreduce CO conversion to undesirably low levels. In embodiments in whichthe zirconia-supported, alkali-metal-modified, ruthenium catalyst isdisposed over a large pore support, the foregoing weight ranges do notinclude the weight of the underlying large pore support.

High surface area ZrO₂ (BET surface area>10 m²/g) is a preferredcatalyst support. While many substitute materials have not yet beentested for use in the inventive catalyst, it is anticipated that manyequivalent substitute materials could be identified in the course ofroutine experimentation. In some embodiments, other metal oxides couldbe used instead of, or in addition to, zirconia. Preliminary testing hasindicated that substitution of these oxides in place of zirconia alsoresults in hydrogen production but at lower conversions.

The catalyst may take any conventional form such as a powder or pellet.In some preferred configurations, the catalyst includes an underlyinglarge pore support. Examples of preferred large pore supports includecommercially available metal foams and, more preferably, metal felts.Prior to depositing the zirconia-supported, alkali-metal-modified,ruthenium catalyst, the large pore support has a porosity of at least5%, more preferably 30 to 99%, and still more preferably 70 to 98%.Preferably, the support has an average pore size (sum of porediameters/number of pores) of from 1 μm to 1000 μm as measured byoptical and scanning electron microscopy. Preferred forms of poroussupports are foams and felts. Foams are continuous structures withcontinuous walls defining pores throughout the structure. Felts arefibers with interstitial spaces between fibers and includes tangledstrands like steel wool. Various supports and support configurations aredescribed in U.S. patent applications Ser. No. 09/640,903 (filed Aug.16, 2000), U.S. Pat. No. ______, which is incorporated by reference.U.S. patent application Ser. No. 09/375,614 (filed Aug. 17, 1999) isalso incorporated herein.

The catalyst with a large pore support (and including thezirconia-supported, alkali-metal-modified, ruthenium catalyst)preferably has a pore volume of 5 to 98%, more preferably 30 to 95% ofthe total porous material's volume. Preferably, at least 20% (morepreferably at least 50%) of the material's pore volume is composed ofpores in the size (diameter) range of 0.1 to 300 microns, morepreferably 0.3 to 200 microns, and still more preferably 1 to 100microns. Pore volume and pore size distribution are measured by mercuryporisimetry (assuming cylindrical geometry of the pores) and nitrogenadsorption. As is known, mercury porisimetry and nitrogen adsorption arecomplementary techniques with mercury porisimetry being more accuratefor measuring large pore sizes (larger than 30 nm) and nitrogenadsorption more accurate for small pores (less than 50 nm). Pore sizesin the range of about 0.1 to 300 microns enable molecules to diffusemolecularly through the materials under most gas phase catalysisconditions.

Certain aspects of the catalyst may be best characterized with referenceto measurable properties of the water gas shift reaction. In somepreferred embodiments, when the catalyst is tested by placement in areaction chamber and contacted with a reactant gas mixture containing 8%CO, 7% CO₂, 38% H₂, and 47% H₂O, at a contact time of 25 ms and atemperature of 420° C., it results in greater than 70% (and in somepreferred embodiments 70 to 85%) CO conversion and at least 80% (and insome preferred embodiments 80 to 95%) CO₂ selectivity. In preferredembodiments where the catalyst contains a large pore support, preferredembodiments of the catalyst can be characterized such that when thecatalyst is tested by placement in a reaction chamber and contacted witha reactant gas mixture containing 8% CO, 7% CO₂, 38% H₂, and 47% H₂O, ata contact time of 50 ms and a temperature of 325° C., it results ingreater than 70% (and in some preferred embodiments 70 to 85%) COconversion and at least 80% (and in some preferred embodiments 85 to100%) CO₂ selectivity.

One preferred method of making the catalyst is by impregnating zirconiawith solutions of Ru and K followed by drying, calcining, and reducing.Other methods could be used. For example, it is also anticipated thatcatalyst with the aforementioned preferred compositions can be preparedby a co-precipitation method using inorganic or organometallic Zrprecursors, Ru and K precursors.

In the inventive method of producing hydrogen gas, a reactant gasmixture comprising carbon monoxide and water vapor is contacted with thezirconia-supported, alkali-metal-modified, ruthenium catalyst. Intypical applications, such as in an portable fuel processing system, thegas mixture will also contain carbon dioxide, hydrogen, and/or inertgases such as nitrogen. In certain preferred embodiments, the gasmixture comprises, in mole % (which is equivalent to partial pressures)1 to 15% CO, 1 up to 70% H₂O, 1 to 15% CO₂, and up to 75% H₂, morepreferably, 3 to 20% CO, 3 to 60% H₂O, 3 to 20% CO₂, and 10 to 60% H₂.It is desired to conduct the water gas shift reaction under conditionsthat minimize the methanation reaction. The water-gas-shift catalyst istypically contained in a reaction chamber. The temperature at thecatalyst during the reaction is preferably less than 450° C., morepreferably in the range of 200 to 420° C., and still more preferably inthe range of 250 to 350° C. to maximize equilibrium CO conversion.Temperature favors reaction rate, but disfavors equilibrium COconversion. Shorter contact times (defined as the total volume ofcatalyst-containing reaction chambers divided by the total volume ofreactant gases corrected to 273K and 1 atm, and assuming ideal gasbehavior) are preferred to minimize reactor volume, preferably less thanIs, more preferably in the range of 3 to 100 ms. Conversion of carbonmonoxide (defined as CO mole change between reactant and product dividedby moles CO in reactant), typically measured in conjunction with theabove-described ranges, is preferably at least 70%; and in somepreferred embodiments conversion is in the range of 50 to 85%.Selectivity to carbon dioxide (defined as moles CO₂ produced divided bymoles CO₂ produced plus moles CH₄ produced), typically measured inconjunction with the above-described ranges and CO conversions, ispreferably at least 70%; and in some preferred embodiments CO₂selectivity is in the range of 80 to 100%.

One embodiment of a reactor 2 is shown in cross-section in FIG. 4. Thereaction chamber 4 contains catalyst 6 and has an inlet 8 and outlet 10.In FIG. 4, the catalyst is shown on the top and bottom of the reactionchamber with an open channel from the reactor inlet to the outlet—thisconfiguration is called “flow-by.” Other configurations, such as“flow-through” where flow is directed through a porous catalyst, are, ofcourse, possible. To improve heat transfer, a microchannel heatexchanger 12 can be placed in contact with the reaction chamber. Themicrochannel heat exchanger 12 has channels 14 for passage of a heatexchange fluid. These channels 14 have at least one dimension that isless than 1 mm. The distance from the channels 14 to catalyst 6 ispreferably minimized in order to reduce the heat transport distance.Microchannel heat exchangers can be made by known techniques such aselectrodischarge machining (EDM).

The preferred reaction chamber for the water gas shift reaction may beof any length or height. The preferred reaction chamber width is lessthan 2 mm. More preferably the reaction chamber width is less than 1 mm.The reaction chamber is preferably in thermal contact with a heatexchange chamber to remove the exothermic reaction heat from the WGSR.The heat exchange chamber in thermal contact with the reaction chambermay also be of any length or height. Preferably the length and height ofthe heat exchange chamber is close to the dimensions of the reactionchamber. Most preferably the heat exchange chamber is adjacent to thereaction chamber in an interleaved chamber orientation (see FIG. 5—widthis the direction in which the interleaved reaction chambers and heatexchange chambers stack). The width of the heat exchanger chamber ispreferably less than 2 mm. More preferably the width of the heatexchange chamber is less than 1 mm. The direction of flow in the heatexchange chamber may be either co-current, counter-current, orcross-flow. This approach will enable excellent heat transferperformance.

The WGS reactor may also be configured by placing the reaction chamberadjacent to a heat exchanger chamber that is comprised of an array ofmicrochannels rather than a single microchannel. In this configurationthe width of the reaction chamber may exceed 2 mm, but at least onedimension of a single microchannel in the array must be less than 2 mm.Preferably this dimension is less than 1 mm. The allowable width of thereaction chamber is a strong function of the effective thermalconductivity of the catalyst insert. The higher the effective thermalconductivity, the wider the insert to enable rapid heat removal. Foreffective thermal conductivites on the order of 2 W/m/, it isanticipated that the maximum reaction chamber width must remain lessthan 2 mm and preferably 1 mm. The advantage of this design approach iseasier manifolding, fluid connections, and catalyst loading; but thisapproach may result in a reduction in heat transfer performance. In somesystem configurations and embodiments the simpler manifolding may resultin a lower system cost that offsets the reduction in heat transferperformance.

In preferred embodiments, the reaction chamber 4 is connected to theoutlet of a primary conversion reactor 16 such that exhaust from theprimary conversion reactor flows into the reaction chamber. Thus, in atypical configuration, fuel and an oxidizer flow through inlet 18 intothe primary conversion reactor 16 where the fuel is converted to CO, H₂Oand CO₂. The primary conversion gases flow out through exhaust port(outlet) 20 and into the reaction chamber where CO and H₂O are convertedto H₂ and CO₂. The product gases (including H₂) then may either flowinto fuel cell 22 where the H₂ is combined with O₂ to generateelectricity, or the product of the WGSR flows into a secondary clean upprocess to remove residual levels of carbon monoxide. The secondaryclean-up process may include a preferential oxidation reactor, membraneseparation of either hydrogen or carbon monoxide, a sorption basedseparation system for either hydrogen or carbon monoxide, and the like.These elements form a highly simplified fuel processing system 30. Inpractice, fuel processing systems will be significantly more complex.Typically, heat from the combustor will be used to generate heat forother processes such as generating steam (not shown) that can beutilized for a steam reformer, autothermal reactor and water gas shiftreactor. Water-gas shift reactors can operate in series. Usually,hydrogen gas from the shift reactor(s) will be purified before it flowsinto the fuel cell. Various fuel cells are well-known and commerciallyavailable and need not be described here. Instead of fuel cell 22, thehydrogen-containing gas could go to: a storage tank, a refuelingstation, a hydrocracker, hydrotreater, or to additional hydrogenpurifiers.

EXAMPLES

The following examples are descriptions based on typical conditions usedto make numerous samples. Certain temperatures, etc. set forth preferredvalues for conducting various steps.

Example 1

5 wt %Ru/ZrO₂ catalyst was prepared by conventional incipient wetnessimpregnation. ZrO2 (6568-45-11F3 ⅛″ extrudates) was obtained fromEngelhard, and ground and sieved into 70-100 mesh. Ru was impregnatedonto the ZrO₂ support to its incipient wetness point (0.4 cc/g) from anaqueous solution of RuCl₃ hydrate (Aldrich, 99.98%). The impregnatedsample was set at room temperature for 30 min prior to drying undervacuum at 100° C. overnight. Finally, the catalyst was calcined underambient conditions with a ramping rate of 5 C/min to 350° C. andisothermally held at that temperature for 1 h.

The water gas shift reaction was carried out in a conventional fixed-beddown flow reactor. The reactor used for powder testing has an insidediameter of 5 mm. Typical catalyst loading was 0.06 gram of 70-100 meshparticles. FIG. 1 shows an example of results from reaction of a gasmixture consisting of 8% CO, 7% CO₂, 38% H₂, and 47% H₂O, over thispowder 5 wt %Ru/ZrO₂ catalyst, at a 25 millisecond (ms) contact time. Ascan be seen in the figure, at 350° C., the conversion of CO is about 90%but the selectivity to carbon dioxide is less than 30%. Thus, Ru on ZrO₂is not a selective water gas shift catalyst when hydrogen is present inthe reactant mixture.

Example 2

An improved powder catalyst, Ru/ZrO₂ promoted with K, was also preparedusing incipient wetness method. Specifically, a 0.5 wt %Ru-1.5% wtK/ZrO₂catalyst was prepared. ZrO₂ (6568-45-11F3 ⅛′ extrudate) was obtainedfrom Engelhard, and ground and sieved into 70-100 mesh. Ru and K wereco-impregnated onto the ZrO₂ support to its incipient wetness point (0.4cc/g) from an aqueous solution of RuCl₃ hydrate (Aldrich, 99.98%) andKNO₃ (Aldrich, 99.99%). The impregnated sample was set at roomtemperature for 30 min prior to drying under vacuum at 100° C.overnight. Finally, the catalyst was calcined under ambient conditionswith a ramping rate of SC/min to 350° C. and isothermally held at thattemperature for 1 h. Again, the water gas shift reaction was carried outin a conventional fixed-bed down flow reactor. The reactor used forpowder testing has an inside diameter of 5 mm. Typical catalyst loadingwas 0.06 gram of 70-100 mesh particles. FIG. 2 shows an example ofresults from reaction of a gas mixture consisting of 8% CO, 7% CO₂, 38%H₂, and 47% H₂O, over this powder catalyst, at a 25 millisecond (ms)contact time. Apparently, K greatly improved the CO₂ selectivity whilestill maintaining superior activity of Ru/ZrO₂ catalyst. For example, ata catalyst bed temperature of about 420° C., the conversion of COreaches about 85% while the selectivity to carbon dioxide is greaterthan 90%.

Example 3

The powdered catalyst described in Example 2 was also investigated invarious engineered forms. Experiments were conducted to demonstrate thepresent invention using 1 microchannel for the water gas shift reaction.The microchannel was placed within a tube furnace to provide therequired preheat for the exothermic reaction. The microchannel was 5-cmlong and 0.94-cm high. The width (or opening) of the microchannel was0.0762-cm or 762-microns. In the case of felt-supported catalyst, 0.0222g of powdered 0.5%Ru-1.5%K/ZrO2 catalyst described in Example 2 wascoated on a metal felt of FeCrAl alloy obtained from Technetics, Deland,Fla. The dimensions of the felt are 1.27 cm in length, 0.94 cm in width,and 0.0254 cm in thickness. The porous structure contained a catalyst of0.5%Ru-1.5%K/ZrO2 powdered catalyst that was prepared by 1) ball-millingthe powdered catalyst 0.5%Ru-1.5%K/ZrO2 (using same method as describedin Example 2) overnight; 2) slurry dip-coated on the FeCrAl felt untilthe desired loading is achieved; 3) the coated catalyst was dried at 90°C. overnight and calcined at 350° C. for four hours. Prior to thecatalyst evaluation, catalyst was reduced in 10%H₂/N₂ (100 cc(STP)/min)at 110° C. for four hours. The felt-supported catalyst was placed insidethe microchannel device as aforementioned.

Engineered foam-supported catalyst was prepared based on foam supportmonolith, which is typically 80-ppi (pores per inch) stainless steel(supplied by AstroMet), with characteristic macropores on the order ofabout 200-μm to 250-μm, and with a porosity of about 90% (by volume).The dimensions of the metal foam monolith are 1.50 cm×0.94 cm×0.0762 cm.The monolith pretreatment consists of cleaning successively indichloromethane and acetone solvents in a water bath submersed in asonication device to agitate the solvent within the monolith.Optionally, the metal surface of the monolith may then be roughened byetching with acid. If this is desired, the monolith is submerged in0.1-molar nitric acid, and placed in a sonication device. The monolithis then rinsed in distilled water and dried at about 100° C. Thefoam-supported catalyst containing 0.0372 g of 0.5%Ru-1.5%K/ZrO2catalyst (prepared using the same method as described in Example 2) wasprepared by 1) ball-milling the powdered catalyst 0.5%Ru-1.5%K/ZrO2(using same method as described in Example 2) overnight; 2) slurrydip-coated on the stainless steel foam metal until the desired loadingis achieved; 3) the coated catalyst was dried at 90° C. overnight andcalcined at 350° C. for four hours. Prior to the catalyst evaluation,catalyst was reduced in 10%H₂/N₂ (100 cc(STP)/min) at 110° C. for fourhours. The foam-supported catalyst was snug-fitted inside themicrochannel device as aforementioned. FIG. 3 shows an example ofresults from reaction of a gas mixture consisting of 8% CO, 7% CO₂, 38%H₂, and 47% H₂O, over these two types of engineered catalysts, at a 50millisecond (ms) contact time. The felt catalyst outperformed the foamcatalyst over the entire range of conditions studied as evidenced byhigher CO conversions and CO₂ selectivities. For example, at atemperature of about 300° C. the felt catalyst gives higher than 85% COconversion with near 100% CO₂ selectivity.

Closure

While preferred embodiments of the present invention have been shown anddescribed, it will be apparent to those skilled in the art that manychanges and modifications may be made without departing from theinvention in its broader aspects. The appended claims are thereforeintended to include all such changes and modifications as fall withinthe true spirit and scope of the invention.

1. A catalyst comprising: a porous substrate having an average pore sizeof from 1 μm to 1000 μm; and disposed over the porous substrate, azirconia-supported, alkali-metal-modified, ruthenium catalyst.
 2. Thecatalyst of claim 1 made by steps comprising: impregnating zirconia withsolution containing Ru and K, calcining, and reducing.
 3. The catalystof claim 1 comprising 0.1 to 10 wt % Ru and 0.1 to 10 wt % K.
 4. Thecatalyst of claim 1 comprising a large pore support wherein at least 20%of the catalyst's pore volume is composed of pores in the diameter sizerange of 0.1 to 300 microns.
 5. The catalyst of claim 4 characterizableby a test in which the catalyst is placed in a reaction chamber andcontacted with a reactant gas mixture containing 8% CO, 7% CO₂, 38% H₂,and 47% H₂O, at a contact time of 50 ms and a temperature of 325° C.,resulting in greater than 70% CO conversion and at least 80% CO₂selectivity.
 6. The catalyst of claim 1 characterizable by a test inwhich the catalyst is placed in a reaction chamber and contacted with areactant gas mixture containing 8% CO, 7% CO₂, 38% H₂, and 47% H₂O, at acontact time of 25 ms and a temperature of 420° C., it results resultingin greater than 70% CO conversion and at least 80% CO₂ selectivity.7-21. (canceled)
 22. The catalyst of claim 1 wherein the poroussubstrate comprises FeCrAlY.
 23. The catalyst of claim 1 comprising 0.2to 3 wt % Ru and 0.1 to 10 wt % K.
 24. The catalyst of claim 23comprising 0.5 to 3 wt % K.
 25. The catalyst of claim 23 comprising ZrO₂with a BET surface area greater than 10 m²/g.
 26. The catalyst of claim1 having a pore volume of 30 to 95%.
 27. The catalyst of claim 23wherein at least 20% of the materials pore volume is composed of poresin the size range of 0.1 to 300 microns.
 28. The catalyst of claim 1wherein at least 20% of the materials pore volume is composed of poresin the size range of 1 to 100 microns.
 29. The catalyst of claim 3wherein at least 50% of the materials pore volume is composed of poresin the size range of 0.3 to 200 microns.
 30. The catalyst of claim 1characterizable by a test in which the catalyst is placed in a reactionchamber and contacted with a reactant gas mixture containing 8% CO, 7%CO₂, 38% H₂, and 47% H₂O, at a contact time of 50 ms and a temperatureof 325° C., resulting 70 to 85% CO conversion and 80-95% CO₂selectivity.
 31. The catalyst of claim 3 characterizable by a test inwhich the catalyst is placed in a reaction chamber and contacted with areactant gas mixture containing 8% CO, 7% CO₂, 38% H₂, and 47% H₂O, at acontact time of 25 ms and a temperature of 420° C., resulting in 70 to85% CO conversion and at least 80% CO₂ selectivity.
 32. The catalyst ofclaim 1 wherein the porous substrate comprises a felt.
 33. The catalystof claim 27 characterizable by a test in which the catalyst is placed ina reaction chamber and contacted with a reactant gas mixture containing8% CO, 7% CO₂, 38% H₂, and 47% H₂O, at a contact time of 50 ms and atemperature of 325° C., resulting 70 to 85% CO conversion and 80-95% CO₂selectivity.
 34. The catalyst of claim 29 characterizable by a test inwhich the catalyst is placed in a reaction chamber and contacted with areactant gas mixture containing 8% CO, 7% CO₂, 38% H₂, and 47% H₂O, at acontact time of 25 ms and a temperature of 420° C, resulting in 70 to85% CO conversion and at least 85% CO₂ selectivity.